Gasoline prepared from cracking hydrodesulfurized residual oil

ABSTRACT

A GASOLINE IS PRODUCED BY ZEOLITIC RISER CRACKING OF A DISTILATE GAS OIL BOILING BELOW 1050*F. TOGETHER WITH AN AMOUNT LESS THAN 25 VOLUME PERCENT OF HYDRODESULFURIZED CRUDE OIL RESIDUE BOILING ABOVE 1050*F. THE PROPORTION IN THE GASOLINE OF THE CRACKED PRODUCTS OF THE HYDRODESULFURIZED RESIDUE OIL CONSTITUTING AN INCREASED VOLUMETRIC GASOLINE YIELD AND ELEVATING THE OCTANE VALUE OF THE LOWEST OCTANE 100*F. BOILING RANGE FRACTION OF THE CRACKED PRODUCTS IN THE GASOLINE DERIVED EXCLUSIVELY FROM THE DISTILLATE GAS OIL BOILING RANGE HYDROCARBONS.

Sept. 10, 1974 M. C. BRYSON ET AL GASOLINE PREPARED FROM CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10, 1972 lo Sheets-Sheet 1 SBARRELS OF |050F+REs|0- UAL OIL NOT VAPORIZED n x N 82 ARRE S OF GAS OIL APORIEED '3BARREL5 OF m I000 w M H A IO50F+RES|D- 0: OIL VAPORIZED 3 1 0: LU TRUE BOILING POIN 900 1 Z m A I II ,"Eoul uBmuM FL SH 2 w PORIZATICN q 800 BASISIIOOBAWRELSOF FEED n I05 "F EOUIL BRIUM TEMPE RATUFE 700 0 I0 so a0 I00 VOLUME PERCENT DlSTILL ED Sept. 10, 1974 c BRYSON ETAL 3,835,023

GASOLINE PREPARED FROM CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10, 1972 10 Sheets-Sheet 2 FIG.2

H 1 4BARRELS OF |O50F+ RESIDUAL on.

N r VAPORIZED -as BARRELS 0F GAS OIL VAPOR ZED BARRELS 0F \IO50F+ IOOO RESIDUAL OIL LL VAPORIZED L3 O: I! a 900 v uJ z Lu r- 800 I K O BASIS 400a \RRELE 0F 0. FEED AT IOEOF EQUILIBRIUM TEMPERAT JRE 0 IO 3O 4O 5O 6O 8O I00 VOLUME PERCENT DISTLLED Sept. 10, 1974 BRYSQN EI'AL GASQLINE PREPARED FROM CRACKING HYDRODESULFURIZED RESIDUAL OIL 10 Sheets-5het a FIG. 3

Filed Jan. 10, 1972 0 m U m D S m R F wm Q m a MI c aa a W 0 Mm? E+P W o E AM Mh w F A 8 OUV 0 O R 3| A5L E m 801 s P I 7 In H M m RFE R M A um m I M um m 33m w cp n w aw BEE W m A 0D W w w W O M I Z w E w m V w M f O O O O O o w w w w m w 1 m w 9 B 7 5 VOLUME PERCENT DISTILLED Sept. 10, 1974 c BRYSQN ETAL 3,835,023

' GASOLINE PREPARED FROM CRACKING HYDRODESULFURIZED RESIDUAL OIL 1O Sheets-Sheet 4 Filed Jan. 1 1972 FIG.4

ii //i CA LYST 11% IITO'F 500 600 700 800 900 I000 H00 I200 TEMPERATURE: 'F

Sept. 10, 114 c BRYSQN ET AL GASOLINE PREPARED FRO CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10. 1972 1051198125-5118812 5 F IG.5

PRESSURE: PSIA 500 600 700 800 900 I000 H00 I200 I300 TEMPERATURE F Sept. 10, 1974 c BRYSQN ET AL 3,835,023

GASOLINE PREPARED FROM CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 1.0, 1972 lo Sheets-Sheet 6 950 F Cracking Research, +3.0g,Leod

R SID E( DS Research, SI E *O.5g,l eod R SI UE' (HD Research, R ID Clear TRUE BOILING POINT-"F Sept. 10, 1974 r M, C BRYSQN ETAL 3,835,023

GASOLINE PREPARED FRO" CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10, 1972 10 Sheets-Sheet '7 FEB] |oo0F Cracking Research, RE (H +3.0g,Leod

RESIDUE-y 98 I Research 96 ,RE-SIDUE HDE) a i +O.5g,.Leod 94 92 GAsc|L R SI UE (HD Research,

Clear TRUE BOILING POINT-F Sept. 10, 1974 Q BRYSON ET AL 3,835,023

GASOLINE PREPARED FRO]! CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10, 1972 10 Sheets-Sheet 8 FIGS 950F Crdcking Motor, +3.09, Lead ES DU (H S Motor,

SID E( DS Motor, Clear SI UE HD TRUE BOILING POINT-"F Sept. 10, 1974 Q BRYSQN ET AL 3,835,023

GASOLINE PREPARED FRO]! CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10. 1972 l0 Sheets-Sheet 9 |o0oF Cracking Motor,

+3.0g,Leud

RE ID (H S) Moior, 84 +O.5g,Leod R SI UE Molor, Clear f ESI UE(HD RE IDU G 8 IL.

TRUE BOILING PO|NT-F p 1974 M. c. BRYSON ETAL 3,835,023 I GASOLINE PREPARED FROM CRACKING HYDRODESULFURIZED RESIDUAL OIL Filed Jan. 10, 1972 10 Sheets-Sheet 10 FIG. I0

I B I I I l RISER EFV TEMP 0F IIOOF 0 II II II II I n n n u u u u VOLUME PERCENT OF VAPORIZED FEED BOILING ABOVE RISER EQUILIBRIUM TEMPERATURE I I I I 20 25 3O 35 4O VOLUME PERCENT OF LIQUID FEED BOILING ABOVE RISER EQUILIBRIUM TEMPERATURE United States Patent 3,835,023 GASOLINE PREPARED FROM CRACKING IIYDRODESULFURIZED RESIDUAL OIL Millard C. Bryson, Conway, Joel D. McKinney, Indiana,

Robert A. Titmus, Pittsburgh, and Frederick K. White, Allison Park, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa.

Filed Jan. 10, 1972, Ser. No. 216,448 The portion of the term of the patent subsequent to Nov. 27, 1990, has been disclaimed Int. Cl. C101 1/04; Cg 11/04 US. Cl. 208-16 14 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the improvemet in octane number of a gasoline product obtained by fluid zeolite catalytic cracking of a feed without added hydrogen comprising hydrodesulfurized residual oil in addition to gas oil.

Newer model automobile engines are designed with lower compression ratios than heretofore in order to utilize no-lead or low-lead gasoline as fuel. These engines sometimes exhibit a hesitation upon acceleration from a full stop. This hesitation arises due to uneven burning of fuel upon surge resulting in low fuel efficiency. This un even burning is due to the presence of the higher boiling gasoline components, i.e. gasoline components boiling above 360 F. or 380 F. up to 400 or 430 F., since these higher boiling components include aromatic types which are difficult to ignite. The difficulty can be corrected by removal of these components, However, the high boiling gasoline components include some of the highest octane components in the full-range gasoline. The present invention tends to mollify the loss in octane value due to omission of 360 F.+ or 380 F.+ material from gasoline when a 360 or 380 F. or lower end point gasoline is being produced by upgrading the octane value of the mid-boiling range fraction of the gasoline, i.e. that fraction of the gasoline boiling in the 125 to 300 F. range, which includes the lowest octane fraction of the gasoline. This elfect occurs independently of blending. When a fullrange (100 F. or C to 400, 430 or 450 F.) gasoline product is being produced the present invention can provide a generally higher octane value over the full-range gasoline product as well as contributing to more uniform octane values between the highest and lowest boiling fractions of the gasoline (the highest and lowest boiling fractions have a relatively high octane value) on the one hand and the middle boiling gasoline fraction (which has a relatively low octane value) on the other hand. Therefore, the present invention has utility in the production of both low end-point gasoline (360 or 380 F.) or standard end point gasoline, i.e. 400 F., or higher.

The presence of hydrodesulfurized (HDS) residual oil in the feed of the present invention provides an improved unleaded octane value in the fraction of the gasoline product boiling between 125 and 300 F., generally, between 150 and 275 F., more specifically, and between 175 and 250 F., most specifically, as compared to the gasoline product from a feed comprising gas oil only and Patented Sept. 10, 1974 as compared to the gasoline product from a feed comprising gas oil plus the same amount of non-hydrodesulfurized residual oil. The improvement is achieved in unleaded and leaded Research and Motor octane value. It is an important advantage of this invention that the gasoline fractions improved in octane value are the fractions of the gasoline product possessing the lowest octane values. Inclusion of the residual or hydrodesulfurized residual feed can also increase the octane value of the lowest and highest boiling fraction of the gasoline product Genereally, however, the degree of improvement is greatest in the mid-boiling fraction. In any event, the full range gasoline values are improved.

The present invention applies to the type of riser cracking systems now in use employing riser outlet temperatures between 900 and 1100 F., a relatively low pressure which is not critical and can be about 5 to 50 p.s.i.g., a residence time of up to 5 seconds and catalyst to oil weight ratios between 4:1 and 25:1, generally, 5:1 to 15:1, preferably, and 6:1 to 12:1, most preferably. Regenerated catalyst temperatures between 1100 F. and 1350 F., generally, and 1225 F. 1325 F., preferably, can be employed. These riser systems operate with catalyst and hydrocarbon feed flowing concurrently into and through the riser at about the same velocity, thereby avoiding any signficant slippage of catalyst relative to hydrocarbon in the riser and avoiding formation of a catalyst bed in the reaction flow stream. In this manner the catalyst to oil ratio does not increase significantly from the riser inlet along the reaction flow stream. The catalyst employed is a fluid crystalline aluminosilicate molecular sieve catalyst. Any catalyst of sulficient activity and/ or selectivity to produce significant feed stock cracking at residence times of five seconds or less are within the purview of this invention.

Four tests were conducted to illustrate the effect of blending non-hydrodesulfurized residual oil into a gas oil distillate feed stream so that residual oil and gas'oil were added together at the bottom of a riser. The tests were performed in a fluid catalytic riser cracking system employing a zeolite catalyst. The unit operating conditions were held as constant as possible throughout all the tests. A uniform fresh feed rate was maintained during the tests. The reactor outlet temperature was maintained at 930 F., the regenerator bed temperature at 1220 to 1235 F. and the feed preheat temperature at 340 to 375 F. Slurry recycle varied between 4.7 volume percent and 8.7 volume percent of fresh feed.

The basic gas oil feed had a 5 percent distillation temperature of 577 F. and a percent distillation temperature of 920 F. and had a gravity of about 24 API. The The residual oil blended into the unit was percent non-hydrodesulfurized South Louisiana vacuum tower bottoms boiling above 1050 F. and having a gravity of 11 API. As shown in Table l, residual charge to the unit was absent in the base case and then was set at three incremental rates: 5.1 volume percent, 10.1 volume percent and 14.7 volume percent of the fresh feed. As the residual oil content was increased from the zero percent residual oil level to the 14.7 volume percent residual oil level, the hydrogen make increased from 0.32 volume per cent to 0.73 volume percent and the coke make increased from 4.93 weight percent only to 5.47 weight percent, which is a very small increase. All of the light end components (methane through butane-butenes) decreased with increasing residual levels from a total volume percentage of 35.67 percent to 25.82 percent. Also, with increasing residual contents, the gasoline yield increased from 60.4 volume percent to 62.0 volume percent. The yield of products heavier than gasoline (light gas oil and decanted oil) showed an increase with increasing residual level, with the greatest portion of the change occurring 3 with highest residual contents in the feed. Finally, with increasing residual feed content the conversion to gasoline and lighter products decreased from 80.2 volume percent to 75.3 volume percent. Selectivity to gasoline (measured as a ratio of gasoline yield to conversion) 4 a lowering of catalyst activity. This deleterious effect occurs in addition to the deposition upon the catalyst of the metals content of the residual oil, especially nickel and vanadium, further tending to reduce catalyst activity and selectivity.

TABLE 1.GASOLINE OCTANE RATINGS Gas oil plus Gas oil plus Gas oil plus Gas oil plus 5.1 percent. of 10.1 percent of 14.7 percent of 0.0 percent, 1,050 F.+ F.+ 1, F. Inspection residual residual residual residual Light gasoline:

Motor octane numbers:

Cle so. 4 so. 0 so. 4 so. 0 +0 53 grams lead... 84. 0 84. 0 82. 9 84. +1 59 grams lead.-. 87. 0 85. 0 84. 3 85. 5 +3.17 grams lead 88. 4 87. 4 S6. 0 86. 5 Research octane numbers:

Clear 92. 0 92. 4 ll. 8 9 5 +3.17 grams lead 99. G 99. 8 100. l 100 5 Heavy gasoline:

Motor octane numbers:

81. 1 80. 7 82. 0 81. 1 83. 6 84. 6 84. O 84. 5 86. 0 85. 6 85. 5 85. 2 +3.17 grams lead 87. 7 87. 2 87. 4 86. 8 Research octane numbers:

Clear 93. 0 92. 8 92. 7 95. 1 98. 6 98. 0 98. 7 98. 5

+3.17 grams lead increased from 0.753 for the gas oil feed to 0.823 for the highest residual-gas oil feed mix of the fourth test. Therefore, if proper conditions are achieved at the onset of the cracking reaction, i.e. at the bottom of the riser, the portion of the feed boiling higher than 1050 F. true boiling point is highly selective towards gasoline production. It yields increased gasoline selectivity in comparison to that yielded from the feed boiling below 1050 F., i.e. typical virgin gas oil distillate, at comparable cracking conditions.

As shown in Table 1, all the octane ratings remained essentially the same during the tests with only one exception. Table 1 shows that adding 5.1 percent or 10.1 percent of 1050 P residual oil to the gas oil feed liquid did not affect the octane number of the gasoline product.

An effect on octane number appeared for the first time when 14.7 percent of 1050 -F.+ residual oil was added to the gas oil feed and then the etfect was apparent only in the heavy gasoline product fraction (unleaded) and not in the light gasoline product fraction. Table 1 therefore indicates that as much as 10.1 percent residual oil had no efiect upon the octane number of either light or heavy gasoline product and an effect did not appear until 14.7 percent of residual oil was added, whereupon the effect was apparent only in the heavy gasoline fraction and amounted to more than two Research octane numbers on an unleaded basis. In the data of Table 1, the light gasoline fraction had a 5 percent temperature of 110 F. and a 90 percent temperature of 234 F. while the heavy gasoline fraction had a 5 percent temperature of 239 F. and a 90 percent temperature of 398 F. It is emphasized that the coke yield varied very little in all the tests, indicating that a uniformly high percentage of the oil was vaporized in each of the tests.

The data of Table 1 illustrate the critical effect upon gasoline product octane value of the amount of residual oil in a gas oil distillate feed stream. FIGS. 1 through 5 illustrate how to determine whether the amount of 1050 F.+ residual oil present in a feed stock to a riser operating at a particular feed-catalyst equilibrium temperature at the riser inlet will provide an octane number improvement in tests as illustrated in Table 1. In order for the residual oil to affect the product octane value, the high boiling residue feed components must vaporize at the riser inlet because only by vaporization can any feed component be cracked to gasoline and other products and exert an advantageous effect upon the process. Most residual feed components that do not vaporize remain on the hot catalyst surface and tend to be converted to coke, thereby resulting in a loss of useful product and vaporization of feed, especially of high boiling residual feed components, if it is to occur, must occur at the riser inlet where the catalyst is fresh from the regenerator and is therefore the hottest and most active and most selective. The riser temperature drops along the riser length due to heating and vaporization of the feed, the slightly endothermic nature of the cracking reaction and heat loss to the atmosphere. Because nearly all the cracking in the system occurs within one or two seconds, it is necessary that feed vaporization occur nearly instantaneously upon contact of feed and regenerated catalyst at the bottom of the riser. Therefore, at the riser inlet, the hot, regenerated catalyst and preheated feed, generally together with a mixing agent such as steam, nitrogen, methane, ethane or other light gas, are intimately admixed to achieve an equilibrium temperature nearly instantaneously. This equilibrium temperature is referred to herein as the equilibrium flash vaporization temperature of the feed because it is in the process of achieving this temperature that all the feed components that are to vaporize do vaporize. At this equilibrium temperature substantially complete heat exchange between all materials fed to the riser is achieved and all these materials achieve about the same temperature level, i.e. the hot, freshly regenerated catalyst is cooled to the equilibrium temperature by contributing the sensible heat required to raise the feed liquid to the temperature of vaporization, by contributing latent heat of vaporization and by contributing superheating heat to heat the vaporized liquid above the temperature of vaporization. At the completion of this heat exchange process at the riser inlet, the catalyst, the mixing fiuid, the vaporized feed and the unvaporized feed are all at about the same temperature, which is the equilibrium flash vaporization temperature of the system.

It is desirable for the equilibrium flash vaporization temperature to be as high as possible in order to vaporize as much of the feed as possible. It is best to achieve this high equilibrium temperature by utilizing a high regenerator temperature. However, the regenerator temperature is limited by many factors inherent in the system such as susceptibility of the catalyst to sintering and deactivation, equipment metallurgical temperature limitations, the amount of carbon on the deactivated catalyst, etc. A much less desirable method of increasing the equilibrium temperature is by arbitrary increase of catalyst feed rate because high catalyst-to-oil ratios are known to reduce selectivity to gasoline product by increasing production of undesirable products. Therefore, in any given reactorregenerator system operating in a heat-balance relation ship the equilibrium flash vaporization temperature should be held to the lowest practical level if an increase must be made at the price of increasing the catalyst-to-oil ratio.

Since the equilibrium flash vaporization temperature is essentially fixed by the regenerator temperature, the oil feed rate, the oil preheat temperature and the catalyst to oil ratio, in accordance with the present invention the quantity of residual oil which is vaporized at a given equilibrium temperature is established by adjusting the proportion of residual oil to gas oil boiling range material in the feed. The equilibrium flash vaporization temperature will be between the regenerated catalyst temperature and the riser outlet temperature. At the equilibrium flash vaporization temperature, essentially all the gas oil boiling range material having a true boiling point above the gasoline product and below 1050 F. will be vaporized and all or most of the 1050 F.+ residual oil will also be vaporized. It is only vaporized material that can be cracked to lighter useful products such as gasoline and furnace oil since, as stated, the unvaporized material tends to be converted to coke on the surface of the catalyst.

In accordance with this invention the amount of hydrodesulfurized residue having a true boiling point above 1050 F. in the gas oil liquid feed is always only a minor proportion (much less than 50 volume percent, preferably less than or to or volume percent) of the hydrocarbon feed, and most preferably between 15 and 21 percent, while the material having a true boiling point below 1050 F. constitutes the remaining, major proportion of the liquid feed. The ratio of 1050 F.+ hydrodesulfurized residue to 400 F. or 430 F. to 1050 F. gas oil feed (gas oil comprises the hydrocarbons boiling above gasoline but below the 1050 F.+ residue) is adjusted in accordance with this invention either by blending a stream of 1050 F.+ hydrodesulfurized residual material into a gas oil distillate stream or by preparing the total feed directly by adjusting the distillation or flash temperature of a total crude or a reduced crude distillation unit preceding hydrodesulfurization. In either case, the proportion of hydrodesulfurized 1050 F.+ residue to lower boiling feed must be sufficiently low on the one hand that at least 90 volume percent of the total feed is vaporized at the equilibrium flash vaporization temperature. Preferably, 95 percent of the total feed is vaporized. Most preferably, at least 98 or 99+ percent of the total feed is vaporized. On the other hand, the ratio of 1050 F.+ hydrodesulfurized residue to lower boiling feed must be sutficiently high in relation to the equilibrium temperature that adequate 1050 F.+ hydrodesulfurized residue is vaporized and thereby available to be cracked to and improve the octane value of the gasoline product as compared to the octane value that can be achieved under the same conditions and at the same equilibrium temperature in the absence of the 1050 F.+ residue. Suflicient residue should be vaporized at least to improve the octane value of the heavy (250 to 400 F.+ B.P.) gasoline fraction and preferably to also improve the octane value of the lighter (100 to 250 F. B.P.) gasoline fraction. If 100 percent of the feed is vaporized at the equilibrium temperature the equilibrium temperature must be sufficiently high so that the proportion of 1050 F.+ vapors in the total vapors is adequate to improve the octane number of the gasoline product.

The criticality to the present invention of slight varia tions in 1050 F.+ residue content in the hydrocarbon feed is appreciated by referring to the accompanying figures. FIG. 1 shows the volume percent of a particular total hydrocarbon feed vaporized at various temperatures. The hydrocarbon feed is the non hydrodesulfurized bottoms of an atmospheric distillation tower employed as an FCC feed. The solid curve shown in FIG. 1 represents the true boiling point characteristics while the dashed curve represents the equilibrium flash vaporization characteristics of the feed. For the feed shown in FIG. 1, there is a substantial difference in the characteristics of the feed according to the two curves and FIG. 1 illustrates that for the purposes of the present invention it is the equilibrium flash vaporization characteristics that are controlling.

Assuming the equilibrium temperature at the bottom of the riser is fixed at 1050 F. by process conditions, then FIG. 1 shows that the feed at the bottom of the riser on a 100 barrel basis will comprise 82 barrels of vaporized gas oil having a true boiling point below 1050 F., 13 barrels of vaporized 1050 F.+ true boiling point residue and 5 barrels of unvaporized residue having a true boiling point above 1050 F. The data shown in Table 1, above, show that the octane improvement effect of the present invention in the particular tests made only begins to become manifest at a residual content in the feed between 10.1 percent and 14.7 percent, and, even then, the octane improvement effect appeared in the heavy gasoline fraction only. Therefore, at an equilibrium temperature of 1050 F. with the feed shown in FIG. 1, the 13 barrels of 1050 F.+ residue which is vaporized would be on the borderline of effectiveness when charging the particular feed shown with the particular catalyst at the particular riser outlet temperature of the tests of Table 1.

FIG. 2 shows an FCC feed stock of only a slightly different composition as compared to the feed stock of FIG. 1. FIG. 2 represents the characteristics of the non-hydrodesulfurized bottoms of an atmospheric distillation or flashing of a crude oil. As shown in FIG. 2, at an equilibrium temperature of 1050 F., on a basis of 100 barrels of feed, 85 barrels of gas oil having a true boiling point below 1050 F. were vaporized, ll barrels of 1050 F.+ true boiling point residual oil were vaporized and 4 barrels of residual oil were not vaporized. Comparing FIGS. 1 and 2, it is seen that feed stocks providing a slightly different extent of residual vaporization at the equilibrium temperature can be prepared, one of which might provide the octane improvement of this invention while the other might not, based upon the conditions of the tests of Table 1.

In sharp contrast to the feed stocks of FIGS. 1 and 2, FIG. 3 shows the true boiling point data and fiash equilibrium data of the non-hydrodesulfurized atmospheric tower bottoms FCC feed stock which is totall unsuitable for purposes of this invention. As shown in FIG. 3, at a 1050 F. equilibrium temperature, on a barrel basis, the feed comprises 60 barrels of gas oil vapor having a true boiling point below 1050 F., only 7 barrels of residual oil vapor having a true boiling point above 1050 F. and 33 barrels of unvaporized residue having a true boiling point above 1050 F. The feed stock of FIG. 3 is unsuitable for use at a 1050 F. equilibrium temperature because more than 10 percent is unvaporized. However, the very important comparison is made bet-ween the feed stock of FIG. 3 and the feed stocks of FIGS. 1 and 2, that there is considerably less 1050 F.+ residue vaporized at the same equilibrium temperature in the case of the feed stock of FIG. 3 than in the case of the feed stocks of FIGS. 1 and 2, even though the feed stock of FIG. 3 contains a considerably higher proportion of 1050 F.+ residue than the feed stocks of FIGS. 1 and 2. FIG. 3 shows that when the quantity of 1050 F.+ residue in the feed exceeds 40 or 50 percent, the amount of 1050 F.+ residue that can be vaporized decreases. Therefore, the present invention does not apply to feeds having excessively high residue contents.

A comparison of FIG. 3 with FIGS. 1 and 2 therefore shows that the amount of 1050 F.+ material vaporized in the riser does not increase merely by increasing the absolute quantity of 1050 F.+ true boiling point material in the feed. The comparison of the figures shows that the amount of 1050 F.+ true boiling point residue actually vaporized at a particular equilibrium temperature can actually decrease by increasing the proportion of said residue in the feed, and vice versa. This is a highly important observation in accordance with the present invention 7 because it is the quantity of 1050 F.+ residue actually vaporized which improves the octane value of the product and it is shown that the quantity of residue vaporized is not necessarily related to the proportion of residue in the feed at a fixed equilibrium temperature.

FIG. 4 is based upon the feed stock of FIG. 1 and FIG. is based upon the feed stock of FIG. 3. FIGS. 4 and 5 relate the percentage of the feed vaprized to both equilibrium temperature and pressure in the riser. FIG. 4 indicates that with a regenerated catalyst temperature of 1170 F. it is possible to obtain a high degree of vaporization with the particular fccd tested. ln contrast, FIG. 5 shows that with a generally similar regenerated catalyst temperature of 1180 F., it is not possible to obtain sulficient feed vaporization to render the particular stock useful as an FCC feed in the process of this invention.

Although the data illustrated in FIGS. 1 through 5 relate to non-hydrodesulfurized residual oils, similar results would appear if the residual oils were hydrodesulfurized.

It has heretofore been well known that hydrogenation of a cracking feed increases conversion to cracked products. For example, aromatics are more refractory during cracking than the corresponding partially or completely saturated ring structures. On the basis of the prior knowledge, it would be expected that any hydrogenation of aromatics which lessened refractoriness would also reduce the octane value of the debutanized gasoline product since addition of hydrogen to aromatics lowers the octane value of the aromatics. It is the unusual feature of the present invention that hydrodesulfurization of a residual feed not only greatly increases the conversion to gasoline during a subsequent gasoline cracking step but also, unexpectedly, greatly enhances the octane value of the gasoline product. Although we are not bound by any theory, one explanation for the octane improvement effect is that during the hydrodesulfurization step or steps he spliting of carbonsulfur bonds in the condensed aromatic ring structures of the high boiling propane-insoluble asphaltene and resin molecules results in a severing of lower boiling aromatics from the high boiling molecules so that there is an in situ net production of gas oil range aromatic hydrocarbons during the hydrodesulfurization process. Since aromatics are known to be high octane gasoline constituents, the gas oil derived from a residue via hydrodesulfurization is likely to be highly superior to a distillate gas oil as an FCC feed. The production of aromatics during residual hydrodesulfurization is shown in Ser. No. 205,791, filed Dec. 8, 1971, J. D. McKinney and J. A. Paraskos, entitled Production of Low Sulfur Asphaltic Fuel Oil, which is hereby incorporated by reference.

The hydrodesulfurization catalyst employed in the process of the present invention is conventional and comprises, for example, Group VI and Group VIII metals on a non-cracking support, Thus, the catalyst may comprise nickel-cobalt-molybdenum or cobalt-molybdenum on an alumina support. The alumina may be stabilized with a l to 5 percent by weight of silica. The preferred catalyst is a nickel-cobalt-molybdenum on alumina containing less than one percent by weight of silica which catalyst may or may not be sulfided. Magnesia is also a non-cracking support. An especially preferred catalyst comprises a particulate catalyst comprising particles between about and ,4 inch in diameter, such as described in US. Pat. 3,562,800 to Carlson et al., which patent is hereby incorporated by reference. The hydrodesulfurization can occur in either one stage or in two stages in series as described in the above-mentioned McKinney et al. application. The hydrodesulfurization process can reduce a hydrocarbon residual feed containing four or more percent by weight percent of sulfur to a product containing one percent, or even 0.5 or 0.3 weight percent sulfur.

The hydrodesulfurization pretreating step for the fluid catalytic cracking feed of this invention occurs with a hydrogen partial pressure of 1,0110 to 5,000 pounds per square inch., preferably 1,000 to 3,000 pounds per square inch. A hydrogen partial pressure of 1,500 to 2,500 pounds per square inch is especially preferred. The gas circulation rate can be between about 2,000 and 20,000 standard cubic feet per barrel, generally, or preferably about 3,000 to 10,000 standard cubic feet per barrel of gas preferably containing 85 percent or more of hydrogen. The mol ratio of hydrogen to oil can be between about 8:1 and 80:1.

The following data are presented to show the advantageous effect of the hydrodesulfurization feed treatment of the present invention in preparing a residual oil for fluid caalytic cracking (FCC).

Data were obtained from tests with a 22 percent reduced Kuwait crude to illustrate that hydrode'siilfurization pretreatment of a residual feed, which is initially unsuitable for use as an FCC charge stock for purposes of the present invention because the ratio of residual hydrocarbons to gas oil hydrocarbons therein is too high, can convert the residual oil into an FCC feed which has a greatly reduced ratio of high boiling residual to gas oil range hydrocarbons. In this manner, an FCC feed is prepared in which the gas oil hydrocarbons are totally or partially derived from the residual oil components in the original feed. If the gas oil hydrocarbons are partially derived from the residual oil components in the original feed, the remainder of the gas oil is either a distillate gas oil or is a portion of the bottoms from the distillation or flashing of the crude from which the residual oil is derived, in which case it is hydrodesulfurized together with the residual oil. The tests were performed with a 22 percent reduced crude initially containing only 10 percent of material boiling below 1000 F. but as desulfurization proceeded through incremental stages the amount of material boiling below 1000 F. which was derived from the l000 F.+ residue increased to 59 percent. The hydrodesulfurization was performed by the method of the aforementioned McKinney et al. application. The results of the tests are shown in the following table.

Icrccut dcsulfurimtion Percent carbon re du Percent asphaltcnes. 15.20-

Ni (p.p.m.) 33. 36 O.

Percent boiling below 10 26.5 44 59 Boiling range 5564, 400 5141,400 5001,400 466-1A00 F. F. F. F.

l 22 percent reduced crude.

The above data show that a residual feed stock initially grossly deficient in gas oil range hydrocarbons for use as an FCC feed stock in accordance with the present invention can be converted into a more useful FCC feed stock which is not only advantageously lower in sulfur, nickel and vanadium contaminants but also is considerably richer in gas oil boiling range hydrocarbons and these gas oil boiling range hydrocarbons are advantageously derived from the original 1000 F.+ residue. The data indicate that considerable gas oil boiling range hydrocarbons can be generated from the original residue. Advantageously, production of gas oil hydrocarbons coincides with removal of contaminants. The amount of gas oil range hydrocarbons generated may be sufiicient to convert the residue to a suitable FCC feed at the desired fiash equilibrium temperature in the FCC riser. Otherwise, the hydrodesulfurization efiluent can be converted to a suitable FCC feed stock upon blending with gas oil boiling range hydrocarbons from an extraneous source, such as a distillate stream.

A series of cracking tests were conducted in a riser with a fluid zeolite catalyst to illustrate more fully the octane improvement advantage of the present invention.

9 All of the tests were performed under the following general conditions:

Cracking temperature: F. 940-1025 Contact time: seconds 0.4-3.6 Reactor pressure: p.s.i.g 23-30 Recycle rate: vol. percent of fresh feed 0-5.0 Catalyst-to-oil ratio: fresh feed 7-12 Regenerator temperature: F. 1140-1160 Carbon on regenerated catalyst: wt. percent 0.15-0.35 Dispersion steam: 1b./ 1,000 lb. catalyst 2-9 Stripping steam: lb./ 1,000 lb. catalyst 4-8 Feed preheat temperature: F. 250-650 The tests were performed with a South Louisiana fullrange virgin gas oil, a South Louisiana non-hydrodesulfurized atmospheric tower bottoms and with the 650 F product of hydrodesulfurization of South Louisiana atmospheric tower bottoms. Following is a description of each of these charge stocks.

,South South Iiydrodesui- Louisiana Louisiana iurizcd A tu1l-' atmos- South range pheric Louisiana. virgin tower atmospheric gas oil bottoms tower bottoms Gravity, API..... 23. 5 21. 8 24. 0 Sulfur, wt. percent 0.58 0. 39 0. 05 Carbon residue, wt. percent- 0. 19 3. ()6 1.40 Total nitrogen, ppm 640 1, 300 1, 000 'Aniline point, F 186 192 204 Nickel, p.p.m 0. 1 4. 7 0. 1 Vanadium, p.p.rn 0. 1 1.2 0. 1 D1160 distillation, F. at-

5 The following is a tabulation of yield based on feed obtained when each of the above charge stocks was jcracked at 1000 F. to obtain 75 percent conversion with a regenerated catalyst temperature of 1140" F.

Atmos- Hydrodesulpheric iurized s Gas tower atmospheric Charge stool: oil bottoms tower bottoms Sulfur, weight percent 58 0. 39 0. 05 Yields, vol. percent, of fresh feed to FCC: Debutanized gasoline 55.5 52.0 56.5 4.7 4.0 2.5 45.0 41.5 45.5 17.5 15.5 18.0 9.0 7.0 7.5 11.0 10.5 12.0 to 0.5 7.5 109.0 104.0 111.5 60

4.0 4.0 3.0 Coke, wt. percent 4. 0 11. 0 0 Selectivity to gasoline: Gaso- ]ine/cor1v{ekrsiloan i 0.74 0.69 0.75 Potentiala y te,vo.percent:

Gland 0.----- 29.7 23.5 26.3 0: through C5 39.4 31.8 31.4 r Total gasoline, v01. percen 60 C1-C4 aik lation- 85.2 75.5 82.8 C1-C5 alkylation 90.4 79.8 85.4

The above table shows that the virgin atmospheric tower bottoms produced less debutanized (C; gasoline and less total C liquid based on FCC feed than a gas oil distillate. This result is to be expected because the ATE is a residue and therefore contains high boiling compounds (not present in a gas oil distillate) which are difficult to vaporize and tend to coat and carbonize a hot FCC catalyst. The residue also contains metals and sulfur which might furthertend to deactivate the catalyst. However, the above table surprisingly shows that the by drodesulfurized atmospheric tower residue (HDS-ATB) when utilized as an FCC feed resulted in a greater debutanized gasoline yield and a greater total C liquid yield than even the gas oil, which is free of residue. This result is surprising because it shows that it is possible to obtain more gasoline range FCC product based on FCC feed from a residue than from a distillate. The results are additionally surprising because data presented above show that the hydrodesulfurization process does not essentially lower the boiling range of the residue. The above table shows that, as expected, the FCC operation is ordinarily not improved by charging an ordinary residue to the FCC riser but, unexpectedly, is improved by charging a residue which is first hydrodesulfurized. v

For the same tests, following is a tabulation of yield based upon the crude from which the FCC feed was derived.

Basis of comparison.-1,000 F., riser cracking to obtain 75 percent conversion B HDS yield of 97.5 volume percent.

In considering the data of the above table it should be understood that when the original crude oil is prepared for feeding to the hydrodesulfurization or FCC unit, a substantial yield of straight run naphtha and lighter material is first flashed from the feed. Only that portion of the feed which boils above the gasoline range must be cracked to the gasoline range in the FCC unit. The above table shows that a distillate gas oil FCC feed contains 32 volume percent of the crude and omits the highest boiling 9 volume percent of the crude which is sent to a coker or a visbreaker. The atmospheric tower feed to FCC contains the heaviest 41 percent of the crude while the hydTFdesulfurized residue feed to FCC contains the same portion of the crude diminished by about one volume percent to account for a 97.5 volume percent yield from the HDS unit. This 97.5 percent HDS yield is very high and is achieved due to the occurrence of very little hydrocracking of carbon to carbon bonds (as distinguished from carbon to sulfur bonds) in the HDS process. The bove table shows that a higher debutanized gasoline FCC yield is advantageously achieved from the hydrodesulfurized residue than from the non-hydrodesulfurized residue. Both the desulfurized and non-desulfurized residue feeds produced a higher FCC yield based on crude than the gas oil feed because the gas oil feed is a distillate and omits the highest boiling nine volume percent of the crude.

Again, for the same tests, the following table presents a tabulation of octane number for both the light and heavy gasoline product fractions. The light gasoline product fraction has a boiling range of about to 250 F. while the heavy gasoline fraction has a boiling range of about 250 to 430 F.

i V Gasoline product I Light Heavy Hydrode- Hydrodc- Atmossulfurizod Atmossulfurized phcric atmospheric sphcric atmospheric Gas tower tower Gas tower tower Charge stock oil bottoms bottoms oil bottoms bottoms Micro octane number:

Research, clear 90.8 92.5 93.1 93.2 94.4 93.!) Research, +0.5 g 94.7 30.3 30.3 05.3 00.7 05.9 a

99. o 101. 2 100. 2 9s. 00.1 99.1 79. o 30. 0 30. o 32. 2 s2. 0 32. 0 33.3 32.4 35.2 33.7 33.3 37.3 33.4 86.9 87.6 86.6 35.7 37.3

11.3 12.5 12.2 11.0 12.4 11.0 I 11.4 14. 4 11.1 11. 0 13. 4 10. 3 L 11.2 14.3 12.0 11.4 13.4 11.3 Vol. percent:

Aromatics 5 7 10 64 59 59 Olefins 29 42 43 5 1s 17 saturates 66 51 47 31 24 The above data show that in accordance with the meth- 25 TABLE 2 0d of the present invention an improvementin octane Ilydrodesullu i Kuwait value is achieved in both the hght and heavy gasohne prodatmospheric tower bottoms not when cracking a residual l -w g chagge Charge stock 0.5% sulfur 1.0 7 51111111- n com are to a wlth the lnve non as P 1 Sulfur weight percent 05 L0 distillate Oll charge wh1ch does not contain residua 01. gcgenemied gmalystimeto 1,120 H20 ower botiser ut t F 11.030 1,030 The higher octane value for the atmospheric t Contact imteyseconds M M toms product is seen to be accounted for by either 1n- Ligrfigasolmez ial o N-cIea 91.3 90.0 creased aromatics, increased olefins or a bench to +3 grams 1mm 9&9 bmatlon of the two. MON-clear---. 73.1 73.3

v +3 grams lead... 2&5. B :85. The urprising feature of the data of the ab e table 3.) Sulmr'wtpemem M06 um resldes 1n the hydrodesulfurized atmospheric tower bot- Heavy gasoline;

0 nd RON-clear 89.7 89,3 toms data which 1nd1cate generally higher ctane a +3grams1m 97.8 95.7 generally h1gher aromaucs and/or olefins content as m 5 tow +3 grams lead... 86. 4 83. 1 compared to non hydrodesulfurized atmospheric er Sum, wtmmenh 007 M9 bottoms. As indicated above, it 1s highly surprising that a 40 conversion 7m 6m Yields, vol. percent. of fresh feed: hydrogenauon pretreatment step, wluch would be expected Dehutanized gasouuenfl 56 1 48. 2 to lower aromatics and olefin content, was found to ace, 1H complish the reverse when followed by a cracking step, C l-g 2-; i.e. increase or at least hold stable aromatics and olefins j 100.2 106:5 content so that a h1gher gasoline yield w th a resldual oil Czandfighter wt percent In L2 feed 15 aCCOmpllShCd together with a gain or at least n cok e omont. 3.3 9.0 loss in octane value of the gasoline product. selecnmy to$150M:Gamma/0"1" s1on 0.8 0.75 Further tests were performed wherein the FCC feed was derived from the atmospheric tower bottoms (ATB) Methane Yield of a Kuwait crude rather than from a South Lourslana The data of Table 2 Shows that the additional degrca crude. Kuwait crudes are much richer in sulfur than domestic crudes. The additional tests are illustrated in Table 2. In one test of Table 2, a 1.0 weight percent sulfur feed from a single stage hydrodesulfurization unit was charged to FCC. In the other test, a 0.5 weight percent sulfur content feed from a two-stage hydrodesulfurization unit was charged to FCC. (The residue feed to each HDS unit contained about 4.0 weight percent sulfur.) Following are the specifications for each FCC feed stock used in the tests of Table -2.

rec CHARGE UALITY of sulfur removal from the residue feed increased FCC debutanized gasoline yield from 48.2 to 56.1 percentfaud increased gasoline selectivity. Table 2 also shows thatas the degree of desulfurization increased the octane number of the gasoline product also generallyincreased.

The advantage of the present invention is illustrated most strikingly in FIGS. 6 through 9. These figurescontain graphs based on the same series of tests tabulated above showing the relationship of both Rearch and Motor Octane Numbers to the particular gasoline product fractions whose mid-points have the indicated truexboiling points for both 950 and 1000' F. r'ise'r. outlet cracking temperatures. The graphs of FIGS. 6 through 9 show that the gasoline product of gas oil crackingexhibitslthe highest octane value at its highest and lowest boiling extremity fractions'but its mid-boiling fraction exhibits' the lowest octane value, indicating a considerable imbalance in octane value in the gasoline product depending upon boiling point. The dip in octane value of the mid-boiling fraction can require that the mid-boiling fraction be further treated for upgrading, for instance, by constituting a reformer feed stock or by recycle to the FCC unit. Otherwise, as has been done commercially,*-the full range gasoline product is split into a high octane blending stock for premium gasoline pool blends and a lower 13 14 octane blending stock for regular gasoline pool blends. a relatively low Research clear and/ or Motor clear octane FIGS. 6 through 9 show that the great advantage of the value as compared to higher and lower boiling fractions residual oil cracking process of the present invention is that in the a oli e of the ra ked rodu t derived exclusively the low octane value mid-boiling fraction is upgraded from the gas oil boiling range hydrocarbons. The proporwithout diminishing the high octane values of the hightion in the gasoline of the cracked prdoucts of the residual and low-boiling extremity fractions, thereby imparting not oil is sufiiciently great to elevate by at least one number, only a higher average to the total gasoline product but or at least two or three numbers, on an unleaded basis, also a better balance to the octane quality of the various the Research and/or Motor octane value of the lowest incrementalboiling fractions throughout the full boiling 25 F., 50 F., or 100 F. boiling fraction of the cracked range of the gasoline product. This effect appears in FIGS. products derived exclusively from the gas oil boiling range 6 through 9 as a tendency of the residual oil fraction to hydrocarbons. The gasoline of this invention can either be somewhat straighten the curve of octane value obtained blended or unblended with other gasoline. It can be leaded from cracking a distillate gas oil at the same flash vap0ribut is advantageously unleaded or contains less "one zation temperature and the straightening occurs by an imgram of lead per gallon, although it can contain a greater provement in the octane value of the gasoline components quantity of lead. having the lowest octane value. Therefore, a great advan- EXAMPLE tage of the present invention will arise in the instance of the introduction of suflicient residual oil to a gas oil distil- The data presented in Table 3 and illustrated in FIGS. late feed to upgrade a mid-boiling fraction of the gasoline 10 and 11 are based upon four FCC feed stocks prepared product to an extent that previous recycling or reforming by atm spheric flashing of portions of a South Louisiana of the mid-boiling fraction is no longer required, although Crude at F: and 3300 p such recycling or reforming can still be performed if y- The bottoms of each crude hash is designated as further octane improvement is desired. Also, the need for cut 1, 3 and 4, respectively, and each cut is vaporized gasoline sphtting or fractionation could be eliminated, if at foul equilibrium temperatures; 1000 1025 desired, since the full range gasoline quality is adequate 1050 and 1100 Th6 data of Table 3 Show, in P for use directly in premium gasoline blends. The residue the distillation data for each Cut and, in P the (HDS) curves of FIGS, 6 through 9 how th t a b tanpercentage of material having a true boiling point above tial further octane number improvement in residual crackthe various riser equilibrium temperatures in both the ing is achieved, in most cases, when the residual feed to feed liquid and the corresponding vapor for each cut.

'Dlstn, F.:

IBP 530 10". 540 606 640 702 750 811 830 88 705 716 760 781 830 857 890 915 825 795 e50 835 910 895 000 955 940 872 963 902 1, 000 900 1,045 1,010 1, 990 1, 1, 016 1, 1, 045 1, 1, 087 E; 1,400 1,

II. FCC Riser Conditions (760 mm. Hg)

Feed cut number v 1 2 3 4 is... equil. temp., 1 1,100 1, 050 1,025 1,000 1,100 1,050 1, 025 1,000 1,100 1,050 1, 025 1,000 1,100 1,050 1,025 1,000

Vol. percent' of liquid feed boiling above riser oquil. temp 1- 11. 0 15. 5 18.5 21.5 12. 0 18. 0 21. 0 24. 5 15. 0 22. 5 26. 0 30. 0 21. 0 29. 5 34. 0 39. 5 Vol. percent of vaporized teed b0 'ng above'riser equil. temp 11. 0 13.5 13. 0 12. 0 12- 0 14. 0 13. 5 12. 0 14. 0 13. 5 12. 0 10. 0 14. 0 11. 0 8. 5 6, 0

FCC is first hydrodesulfurized. FIGS. 6 through 9 show 55 The curves of FIGS. 10 and 11 are based upon the that of all the feed stocks tested the hydrodesulfurized data of Table 3. These curves illustrate the high degree residual oil feed is the most capable of achieving the highof interdependence between the concentration of residue 1y desirable result of a relatively even octane number in gas oil boiling range hydrocarbons in the feed liquid quality over the entire boiling range of the gasoline prodon the one hand and the equilibrium flash vaporization uct and is most capable of removing the octane number 60 temperature at the bottom of an FCC riser on the other difierental between the mid-boiling and high and lowhand if an amount of residue is to be vaporized at the boiling extremes of the full gasoline boiling range product. bottom of the FCC riser which is sufiicient to enhance FIGS. 6 through 9 show that the present invention is the octane value of the gasoline product. Assuming an capable of producing a gasoline having improved uni- FCC process wherein an improvement in gasoline octane formity of octane number along its boiling range com- 65 value requires that more than 14 percent of the vapor at prising the cracked products of a single flash vaporization the bottom of the FCC riser have a true boiling point of a hydrodesulfurized crude oil bottoms comprising both above the equilibrium flash vaporization temperature (as gas oil boiling range hdyrocarbons having a true boiling indicated by line A in FIGS. 10 and 11), it is shown in point below 1050 F. together with residual oil having FIG. 10 that of the four feeds tested only one is capable a true boiling point above 1050 F. The cracked products 70 of providing a vapor adequately rich in residue hydroof the gas oil boiling range hydrocarbons are present in carbons while it is shown in FIG. 11 that of four flash the gasoline in greater proportion than the cracked prodequilibrium temperatures tested, only one is capable of nets of the 1050 F.+ residual oil. A middle-boiling fracproviding a vapor adequately rich in residue hydrocartion of the cracked products in the gasoline derived exbons to achieve the octane improvement of the invention.

clusively from the gas oil boiling range hydrocarbons have 7 5 FIG. 10 shows that cut 4, which is the FCC liquid feed which is richest in residue hydrocarbons of the four cuts tested, is not capable of producing a fiashed vapor adequately rich in residue hydrocarbons. This is indicated by the fact that the curve representing cut 4 does not extend above line A of FIG. 10, although the curve of cut 3, which is poorer in residue, does extend above line A. FIG. 11 shows the high degree of interdependence between the residue concentration in the feed liquid and the riser equilibrium flash vaporization temperature because in the uppermost curve of FIG. 11, which is the only curve which extends above line A, only a feed containing between about 15 and 21 volume percent of residue boiling above the equilibrium temperature can produce a corresponding concentration of residue in the vapor which exceeds line A.

The cross-hatched area B of FIG. defines the intermediate concentration range of residue in the feed liquid above and below which range the corresponding concentration of residue in the vapor is not sufficiently high to achieve the required octane improvement in the present example. FIG. 10 shows that the required corresponding concentration of residue in the vapor is not achieved unless the feed liquid contains a very narrowly circumscribed concentration range of said residue, i.e. a minimum of volume percent of said residue and a maximum of 21 volume percent of said residue.

A surprising observation regarding FIG. 11 is that as the equilibrium flash vaporization temperature increases, it is necessary to decrease the concentration of residuum in the feed and this combination of changes tends to increase the corresponding optimum percentages of the vapor having a true boiling point above the equilibrium temperature. Therefore, according to the present invention, the required concentration of residue in the feed liquid trends downward as the equilibrium temperature increases. FIG. 11 indicates that with the particular feed stocks shown the concentration of residue in the feed preferably should be below volume percent, i.e. the feed preferably should comprise at least 75 percent of gas oil. Therefore, FIG. 10 and FIG. 11 both show it is possible to optimize residue content in the vapor by decreasing residue content in the feed liquid.

The advantage of an awareness of the method of this invention is further emphasized by comparing points C and D of FIG. 11. Although both points represent 14 percent of residue material in the vapor, point C accomplishes this residue vapor concentration with only 15 percent of residue material in the liquid feed while point D accomplishes this vapor concentration with 21 percent of residue in the feed. Since the additional residue at point D will not be vaporized, it will tend to deposit on the hot catalyst and become coke. Therefore, the extra six percent of residue in the liquid feed at point D results in a higher coke make at point D than at point C. Where the FCC unit can achieve a heat balanced operation at a desired regenerated catalyst temperature, it is therefore apparent that the best mode of operating the present invention is to operate closer to point C than point D.

We claim:

1. A zeolite cracked gasoline substantially free of components boiling above 380 F. and having improved uniformity of octane number along its boiling range, said gasoline comprising the cracked products of a flash vaporization of gas oil boiling range hydrocarbons having a true boiling point below 1050 F. together with an amount less than 25 volume percentofhydrodesulfurized residual oil having a true boiling point above 1050?.,E. a middle boiling fraction of the cracked products in the gasoline derived exclusively from the gas oil boiling range hydrocarbons having a relatively low Research clearor Motor clear octane value as compared to higher and lower boiling fractions in the gasoline of the cracked products derived exclusively from gas oil boiling range hydrocarbons, the proportion in the gasoline of the cracked products of the hydrodesulfu'rized residual oil both increasing the percent by volume of gasoline yield as compared to zeolite cracking of said gas oil exclusively and elevating by at least one number on an u'rileaded basis either the Research or the Motor octane value of the lowest octane F. boiling range fraction of the cracked products in said gasoline derived exclusively from the gas oil boiling range hydrocarbons. I

2. The gasoline of claim 1 wherein the proportion of cracked products of the hydrodesulfurized residual oil is sutficiently great to elevate by at least one number both the Research and Motor octane value of the lowest octane 100 F. boiling range fraction of the cracked products derived exclusively from the gas oil boiling range hydrocarbons.

3. Claim 1 wherein the gasoline is substantially free of components boiling above 360' F.

4. The gasoline of claim 1 in a blend with other gaso line. 5. The gasoline of claim 1 unblende'dwith other gaso line.

6. The gasoline of claim 1 in an unleaded condition.

7. The gasoline of claim 1 containing lessthan 1gram of lead per gallon.

8. The gasoline of claim 1 wherein said lowest octane boiling range fraction has a 50 F. boiling range.

9. The gasoline of claim 1 wherein said lowest octane boiling range fractionhas a.25f.Fr boiling,range.

10. Claim 1 wherein the gasoline comprises: "the cracked products of a fia'sh vaporization qfithe'bo'ttoms of a crude oil distillation which bottoms contain. both gas oil hydrocarbons and the hydrodesulfurize'd'residual oil of the crude.

11. Claim 1 wherein the gasoline comprises the cracked products of a. flash vaporization of a blend of gas oil distillate and hydrodesulfurized residual oil.

12. Claim 1 wherein the Research clear octane value is elevated at least two numbers.

13. Claim 1 wherein the Research clear octane value is elevated at least three numbers.

14. Claim 1 wherein the amount-of hydrodesulfurized residual oil having a boiling point above 1050 P. which is flash vaporized with gas oil is 15 to 21 volume percent.

References Cited UNITED STATES PATENTS 

